<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">

<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <title>判断数字是否为两位数</title>
    <style>
    body {
        font: 12px/1.5 arial;
        text-align: center;
    }
    
    .f-text {
        width: 50px;
        border: 1px solid #ccc;
        background: #f0f0f0;
        font-family: inherit;
        padding: 3px;
        margin-right: 10px;
    }
    </style>
    <script type="text/javascript">
    window.onload = function() {
        var aInput = document.getElementsByTagName("input");
        var aSpan = document.getElementsByTagName("span")[0];
        var i = 0;

        aInput[0].onkeyup = function() {
            this.value = this.value.replace(/[^\d]/, "")
        }

        aInput[1].onclick = function() {
            (aInput[0].value == "") ?
            alert("请输入数字！"):
                alert(/^\d{2}$/.test(parseInt(aInput[0].value)) ? "√ 是两位数" : "这是" + aInput[0].value.length + "位数");
        }
    };
    </script>
</head>

<body>
    <input type="text" class="f-text" />
    <input type="button" value="是否为两位数" />
</body>

</html>
